1. Technical Field
This disclosure relates generally to shafts within a gas turbine engine in general, and to flexible shafts used within a gas turbine engine having an epicyclic gear train in particular.
2. Background Information
Gas turbine engines typically employ an epicyclic gear train connected to a turbine section of the engine, which is used to drive the fan section. In a typical epicyclic gear train, a sun gear receives rotational input from a turbine shaft through a compressor shaft. A carrier supports intermediate gears that surround and mesh with the sun gear. A ring gear surrounds and meshes with the intermediate gears. In arrangements in which the carrier is fixed against rotation, the intermediate gears are referred to as “star” gears and the ring gear is coupled to an output shaft that supports the turbo fan. In arrangements in which the ring gear is fixed against rotation, the intermediate gears are referred to as “planetary” gears and the carrier is coupled to the output shaft that supports the turbo fan.
During operation, forces and torque transferred through the epicyclic gear train can create tremendous stresses within the gear train components, making them susceptible to breakage and wear, even under ideal conditions. These stresses can be exacerbated in instances where there is an axial misalignment or shift between the sun gear and the shaft. Such axial misalignments and shifts can be induced by imbalances in rotating hardware, manufacturing imperfections, and transient flexures of the shafts and support frames due to aircraft maneuvers. Consequently, there is a need in the art for a flexible shaft that can accommodate such axial misalignments and shifts, while still maintaining adequate torsional rigidity to drive the epicyclic gear train.